1. Field of the Invention
The present invention relates to a system or to an apparatus that is used for monitoring the shape of an insertion portion or a flexible tube of an endoscope that is inserted inside a cavity or a hollow of an object.
2. Description of the Related Art
It is beneficial for an endoscopic operator to grasp the shape of a flexible tube of an endoscope that is inserted inside a body. In particular, the visualization of the endoscope shape inside the body has a significant advantage when operating a lower intestinal endoscope, such as a colonoscope, since insertion of the flexible tube into a tortuous intestine is difficult. As a result, various types of endoscope-shape monitoring systems have been proposed.
A system that uses an alternating magnetic field for detecting a shape of a flexible tube of an endoscope is conventionally known. In this system, a plurality of coils are disposed along the longitudinal direction of the flexible tube, and a three-dimensional position and a direction for each of the coils are detected by using electromagnetic interactions between the alternating magnetic field and the coils. For example, the shape of the flexible tube is represented by a three-dimensional spline curve, which is obtained from position data of measurement points where the coils are placed, and the result is displayed on a monitor.
However, it is not easy for a user to grasp the shape of the flexible tube when the shape is merely represented by a simple curve or a simple line graph, since the flexible tube has an actual thickness. Thus, in U.S. Pat. No. 5,253,647, the shape of a flexible tube is described as a tube with a thickness so as to suit the actual shape of the flexible tube.